A. Sharks store enough urea to match the total solute concentration of the surrounding seawater
Regurgitation influences the flow of blood by mixing the oxygen-poor blood with the oxygen-rich blood. Due to this, the heart has to pump more to oxygenate the entire body, leading to the rapid, and fluttering heartbeat. The tissues get oxygenated but regurgitation could be fatal, as the heart cannot function overtime forever.
Valve prolapse influences the flow of blood when the flow of blood backs up. This leads to an irregular or racing heartbeat. Even at certain occasions, the blood can flow back to the lungs. However, there is not a huge influence in the oxygenation of the body tissues.
Stenosis makes the ventricles to pump overtime to get enough blood through, and in the process, the ventricles thicken. This functions for a while, however, it will result in heart failure as the heart cannot do it for entire life. The tissues are oxygenated, but it will be an issue due to overtime.
They protect bacterial cells from white blood cells.
